1. Field of the Invention
The present invention relates to a lens control system and, more particularly, to a lens control system in which a movable lens such as a focusing lens is controlled according to an operation on an endlessly turnable operating member in lens control for a television lens apparatus or the like.
2. Description of the Related Art
A lens apparatus such as a one-rod unit/servo unit combination lens capable of changing operating units used for lens operation, a lens apparatus such as an automatic focusing (AF)/manual focusing (MF) selectable lens capable of changing focusing control between AF and MF and other lens apparatuses are known as television lens apparatuses.
For example, a one-rod unit/servo unit combination lens is arranged so that an operating unit used for lens operation can be selected from a one rod-two operations operating unit incorporated in a lens unit and a servo operating unit connected via a cable or the like. In the one rod-two operations operating unit, the focus position is changed when a one rod-two operations rod is turned, and the zoom position is changed when the one rod-two operations rod is pushed or pulled. In the servo operating unit, the focus position or the zoom position is changed when an operating member of a controller (a focus demand or a zoom demand) ordinarily used for servo control is operated. The one rod-two operations operating unit is ordinarily constructed as a mechanism through which an operating force applied to the one rod-two operations rod is mechanically transmitted as power for focusing (a focusing lens) or zooming (a zoom lens). As a one-rod unit/servo unit combination lens, those with a mechanism for servo control of focusing and zooming are also known in which servo control on focusing and zooming is performed for the operation of one rod-two operations rod by detecting the rotational position and pushed/pulled position of the one rod-two operations rod with position sensors.
Focusing operating units used in lens apparatuses capable of changing operating units and selecting between AF and MF include those having an endlessly turnable focusing operating member such that no end is provided as a limit to the range of turning of the focusing operating member. In such endless-type focusing operating units, detection of the rotational position of the focusing operating member is performed not by an absolute position detection type of position sensor such as a potentiometer but by a relative position detection type of position sensor (encoder) such as an incremental-type rotary encoder. This arrangement ensures that when operating units are changed or the focusing system is changed from AF to MF, the focus position set before the change is effectively taken over to enable the focus to be changed from the position at the time of change of the units according to the amount of operation (the amount of change in rotational position) of the focusing operating member thereafter performed. In such a case, since the focusing operating member is endlessly turnable, a drawback of limiting the originally set movable range of the focus by an end of the focusing operating member can be eliminated.
With the focusing operating member capable of endlessly turning as described above, there is a possibility of the focusing operating member being turned beyond the movable range of the focus (the range between the point-blank position and the infinity position in the mechanical construction of the focusing lens) because of the lack of turning limits. An operation performed as such turning to further turn the focusing operating member outwardly from the rotational position reached by the focusing operating member when the focus reaches the end (in a direction toward a point outside the end of the movable range of the focus) is ineffective and the focus position is fixed at the end position.
In the conventional art, even when the focusing operating member is turned so that one of the ends of the movable range of the focus is exceeded, the amount of operation of the focusing operating member turned outwardly in correspondence with the section outside the movable range is treated as zero. Therefore, when the focusing operating member is thereafter turned in the opposite (inward) direction (in the direction of movement of the focus toward the opposite end), the focus simultaneously moves toward the opposite end. In the case of focusing while viewing a picture in a viewfinder or the like, the above-described focusing operation is preferred because it ensures a reduction in the useless amount of operation.
[Patent document 1] Japanese Patent Application Laid-Open No. 11-23943
In some cases of actual use in image-taking jobs, a procedure may be used in which a focusing operating member of a focusing operating unit is operated before actual image taking for example to set a best-focus position or a desired focus position with respect to a subject to be imaged, and a mark is attached to the focusing operating unit to enable the desired condition to be instantly reproduced. For example, when the best focus is obtained, marks formed by a tape or the like are respectively attached in positions aligned with each other to the focusing operating member and a member supporting the focusing operating member, which member move relative to each other. Even if the focus is moved to a different position at the time of actual image taking, the focus may be instantly set at the best focus position confirmed in advance by referring to the mark attached to the focusing operating unit.
In a case where an endless-type focusing operating unit in which a focusing operating member such as that described above is endlessly turned is used, there is a problem that the method of attaching a mark to the focusing operating unit to enable reproduction of the desired focus position cannot be effectively used. That is, after the focusing operating member has been turned beyond a limit corresponding to one of the ends of the movable range of the focus, the focusing operating member may be operated in the opposite direction. In such a case, the amount of operation of the focusing operating member turned beyond the limit corresponding to the end of the movable range of the focus (the amount of over-operation) is treated as zero. For this reason, the marked focus cannot be reproduced even when the positions of marks attached to the focusing operating member and the member supporting the focusing operating member as described above are aligned with each other.